Reduced length free piston engine



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C. P. KOLTHOFF, JR

REDUCED LENGTH FREE PISTON ENGINE Filed Dec. l0, 1956 Aug. 4, 1959 INVENTOR.

BY PLM 2,897,803 REDUCED LENGTH EREE PlsroN ENGINE C. Paul Kolthoi, Jr., Naperville, Ill., assignor to Interiational Harvester Company, a corporation of New ersey Application December 10, 1956, Serial No. 627,296

3 Claims. (Cl. 123-46) This invention relates to internal combustion free piston power plants. More specifically this invention relates to an improved piston and cylinder ring construction for free piston engines.

It is a prime object of this invention to provide an improved free piston engine of reduced overall dimensions.

Still another object is to provide a free piston power plant having improved piston and casing structures wherein the overall length of the free piston engine is greatly reduced over conventional devices.

A still further object is to provide an improved bounce chamber design and compressor piston structure for a free piston power plant.

A still further object is to provide an improvement in 'cylinder rings for free piston engines for effectively sealing the bounce chamber from the power piston cylinder structure and for permitting a decrease in the overa lengthY dimension of the power plant.

These and further objects will become more readily apparent from a reading of the specication when examined in connection with the accompanying sheet of drawing.

In the Ldrawing:

Figure 1 is a cross-sectional view through an improved free piston engine showing various portions thereof in schematic form;

Figure 2 is an exploded view of an improvement in cylinder rings and a contractor for said rings; and

Figure 3 is a fragmentary enlarged cross-sectional view showing a portion of a casing construction of a free piston engine with details of the mounting of a plurality of cylinder rings adapted to engage a power piston structure.

Referring now particularly to Figure 1 a free piston engine is referred to by the reference character 10. The engine 10` comprises a casing 11 having an elongated cylinder 12 provided centrally therein with a combustion chamber 13. The combustion chamber 13 is in communication with a fuel injection nozzle 14 adapted to direct fuel into the combustion chamber 13 in a conventional manner from a suitable source (not shown). The cylinder 12 is also in communication with an exhaust passage 15 which may direct gases under pressure to suitable power converter such as, for instance, a gas turbine, etc.

The casing 11 is also provided at opposite ends of the cylinder 12 with opposed energy accumulating, or what is generally known as bounce chambers 16. Each energy accumulating or bounce chamber 16 is provided with outer end walls 17 and a cylindrical wall 18. The cylindrical wall 18 is provided with suitable valves 18 which are adapted at certain times to permit the entrance of air into portions of the bounce chamber 16. Each chamber 16 is also provided with an inner wallgenerally designated at 19. The casing 11 is also provided with a cylindrical casing portion 20 which surrounds a central portion of the cylinder 12 and also surrounds the cylindrical walls 1S. The cylindrical casing portion 20 is also provided with a plurality of openings 20 permitting the entrance of air for communication with the valves 18.

The walls 19 as indicated are provided with a frusto ite States Patent "ce 2,897,803 Patented Aug. 4, 1959 conical portion 21 which also may be described as an annular tapered portion converging in a direction toward the accumulating chambers 16. As indicated major portions of the inner wall 19 extend laterally with respect to the axis of the cylinder 12 and are disposed longitudinally inwardly from the said cylinder 12. The inner wall 19 separates the [bounce chamber 16 from a compressed air chamber 22. Valves 23, schematically shown, permit the entrance of air by inward compression from certain portions of the bounce chambers 16 to the compressed air chambers 22 during a certain phase of operation of a free piston engine. The compressed air chamber 22 is at times in communication with the cylinder 12 by means of openings 24 provided in the said cylinder.

A pair of power pistons 25 are mounted for reciprocation within the cylinder 12. The power pistons 25 are provided at their ends, nearest to the combustion chamber 13, with conventional piston rings 26.

Compressor pistons 27 are positioned for reciprocation within the bounce chamber 16. The compressor pistons 27 are provided with conventional piston rings 28. Bolts 29 suitably connect the compressor pistons to the power pistons 25. Each compressor piston is provided with an annular tapering portion 39 having an annular sloping surface 31 which slopes or diverges in a idirection outwardly from the axis of the piston 27 and conforms generally and substantially complements the frusto-conical portion 21 of the inner wall 19. Thus in effect the compressor piston 27 may be said to nest with respect to the inner wall 19.

The cylinder 12 is provided at its opposite ends with a plurality of spaced annular recesses 32. As best shown in Figure 3 pairs of cylinder rings 33 are disposed on opposite sides of a spacer plate 33. A plurality of cap screws 34 suitably connect a lower portion of the frusto conical wall 21, and the spacer plate 33 to end portions of the cylinder 12. -Thus the cylinder rings 33 are suitably connected to the ends of the cylinder 12 within the recesses 32.

The cylinder rings 33 may also be termed piston engaging rings and are of split construction with spaced ends 34. It is of course desirable and necessary that the rings 33 engage the outer peripheral surface of each power piston 25 so that the parts 24 are sealed with respect to the compressed air chambers 22. For this purpose a contractor ring 35 is provided for each pair of rings 33. The contractor ring 35 as best shown in Figure 2 comprises annular laterally spaced members 36 suitably connected as indicated at 37. The members 36 are of spring steel material and are of undulating shape so that certain portions thereof engage the recessesV 32 and other portions thereof engage the rings 33 and lforce the rings 33 tightly against the other peripheral surface of the power pistons 25. The split ends 34' of the rings 33 are positioned 180 apart and are suitably held in position by means of inwardly extending fingers 38 on the members 36 which are disposed between the split ends of the ring to thus keepy the rings 33 against relative turning movement and to effectuate about the outer peripheral wall of each power piston 25 complete and eiective sealing.

The free piston engine 19 is provided with a conventional synchronizing mechanism 39 designed to provide for-synchronism movement of each of the pistons 25. For this purpose rack bars 40 are provided, the same rack bars 40 being suitably supported in a guide cylinder 41 suitably supported on the casing 11. A pinion 42 is suitably mounted on a shaft 43supported in a boss 44, the said pinion 44 being engageable with each of the rack bars 40 to effectuate proper synchronised movement of the rack bars 40 and the said pistons 27 and 25. The rack bars are each suitably connected through an opening 45 in the portion 21 of the Vwall 19 to the compressor piston Z7 by means of a threaded stud 46 suitably connected by means of nuts 47. Only one such connection is shown to one of the compressor pistons 27, the other connection of the rack bar 40 to the opposite compressor piston 27 being of course identical. Y

pistons in an outward direction airis drawn into the valves 18 into portions of the bounce chamber'l disposed between the pistons 27 and the walls 19. The compressed air chambers 22 are filled with compressed air and as Vthe power pistons 25 move in an outward direction the ports or openings 24 are uncovered and air rushes into Ythe combustion chamber 13 scavenging the same and exhausting the gases to the exhaust passage 15. In view of the highly compressed air or energy which is stored within the bounce chamber 16 the pistons 25 and 27 are now again moved inwardly toward the combustion chamber 15. During this inward movement the Valves 23 are opened and air is directed from portions of the bounce chamber 16 under pressure into the compressed air chamber 22 thus constantly filling the same with compressed air. The said chamber 22 is now again sealed from the combustion chamber 13 since the power pistons 25 have moved again to the position shown in Figure l. The rack bars 40 are of course eective to provide for continual synchronous movement of the said piston structures. Thus the conventional operation of a free piston engine has been described.

In the conventional free piston engine the power pistons are generally provided with conventional piston rings such as indicated at 26. The opposite ends of the power piston 25 in conventional engines are also provided with similar rings which are also mounted on the piston and engage the walls of the cylinder. In such a conventional construction it is of course obvious that the cylinder is extraordinarily long since, when the compressor pistons are moved to their maximum outward position the piston rings must still be in engagement with the cylinder to properly seal the bounce chamber from the combustion chamber and from the compressed air chamber. Thus in effect the cylinder in conventional engines generally must be much longer than that which is indicated in the present invention. Furthermore, in conventional free piston engines the compressor piston has its inner wall substantially perpendicular to the axis of the piston and cylinder construction. Likewise the wall which normally separates the bounce chamber from the compressed air chamber likewise is a substantially vertical or perpendicular wall with respect to the axis of the cylinder. Such a structure of course also requires increase in length of the overall design of the engine to accommodate the shape of the said piston and wall structures. In effect therefore the conventional free piston engine is generally extremely long in overall length and thus many practical difficulties are encountered in incorporating an engine of this type into a compact space or power plant structure.

The use of free piston engines in connection with the propulsion of gas turbines is becoming more prevalent and thus the future contemplation is therutilization of this type of power package in connection with tractors, cars, buses, trucks and other road vehicles. The problems of size and space in units of this type are, of course, exceedingly acute and it is very desirable to provide power units of such reduced size that payload area, etc., may be correspondingly increased. Applicant has achieved the ob- `jects of this invention, namely, to provide a` reduced size Ytioning of his sealing or cylinder rings in the manner inthe said walls diverging in a `direction toward each other,

dicated whereupon the cylinder size of the engine can be effectively reduced from conventional engines. The reduced cylinder size 12 of course is directly responsible for reducing the overall length dimension of the engine. Likewise the novel shape of the wall 21 and its relation to the novel compressor piston shape causes nesting of the latter with the former so that again the effective lengthwise dimension of the engine is reduced. Thus a reduced size power package will result which can be effectively incorporated in limited areas such as found in road vehicles and other similar devices.

Thus it is believed that the advantages and objects have been generally and effectively described and it should be well understood that the invention is not limited in scope only to the preferred embodiment shown, but that other embodiments and changes may be made without departing from the spirit of the present invention as comprehended within the scope of the appended claims.

yWhat is claimed is:

1. A free piston engine comprising a casing having a cylinder, energy accumulating chambers on said casing disposed at opposite ends of said cylinder, said accumulating chambers each having an outer wall and an inner wall Vlongitudinally spaced from said outer Wall, a compressed air chamber adjacent each inner wall, said compressed air chamber being positioned between said accumulating chambers, said inner walls being of generally frusto-conical shape, tapering generally outwardly and away from said accumulating chambers, valves on said frusto-conical inner Walls adapted to provide for communication between said compressed air and accumulating chambers,

portions of said inner walls being disposed longitudinally inwardly from the ends of the cylinder, a pair of longitudinally opposed power pistons in said cylinder for reciprocation therein, a compressor piston connected to each power piston, each compressor piston being positioned for reciprocation within said accumulating chamber, and an outer wall and inner wall on each compressor piston, the inner wall of each compressor piston being of frustoconical shape and generally complementing the inner wall of each accumulating chamber in at least one position of said pistons.

' 2. A free piston engine comprising a casing having a cylinder, energy accumulating chambers on said casing disposed at opposite ends of said cylinder, said accumulating chambers each having an outer wall and an inner wall longitudinally spaced from said outer wall, a compressed air chamber adjacent each inner wall, said compressed air chamber being positioned bet-Ween said accumulating chambers, portions of said inner walls diverging laterally outwardly of and being disposed longitudinally inwardly from the ends of the cylinder, valves on said frusto-conical inner walls adapted to provide for communication between said compressed air and accumulating chambers, a pair of power pistons in said cylinder for reciprocation therein, a compressor piston connected to each power piston and being positioned for reciprocation within said accumulating chamber, and an outer wall and an inner wall on each compressor piston, the inner wall of each compressor piston being of frusto-conical shape and generally complementing the inner wall of each accumulating chamber in at least one position of said pistons.

3. A free piston engine comprising a casing having a cylinder, energy accumulating chambers on said casing disposed at opposite ends of said cylinder, said accumulating chambers each having an outer wall and an inner wall longitudinally spaced from said outer Wall, a compressed air chamber adjacent each inner wall, said compressed airchamber being positionedy between said accumulating chambers, said inner wall being of truste-conical shape,

valves on said frusto-conical inner Vwalls adapted to provide for communication between said compressed air and accumulating chambers, Va pair of power pistons in said cylinder for reciprocation therein, a compressor piston 5 connected to each power piston, each compressor piston being positioned for reciprocation Within said accumulating chamber, and an outer wall and an inner Wall on each compressor piston, the inner Wall of each compressor piston being of frusto-conical shape and generally complementing the inner wall of each accumulating chamber in.

at least one position of said pistons.

References Cited in the le of this patent UNITED STATES PATENTS 820,222 Livingston May 8, 1906 (Addition to N0. 434,061) 

